Police Commissioner Bernard Hogan-Howe visited a school in Edmonton today to highlight the dangers of knife crime.
The school was hit by tragedy a year ago when a 15-year-old pupil at Edmonton County School was stabbed to death in the street.
Negus McClean bled to death from wounds to his chest and thigh as his 13-year-old brother Elijiah wept at his side.
Negus was trying to stop a gang from stealing his brother's mobile phone when the attack happened.
The pair were chased by up to nine masked youths on bicycles in April last year after they went out for a takeaway.
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The chimes are being stopped to allow extensive renovation work to the Elizabeth Tower, the Great Clock and its bell.